The present invention relates generally to simple, single-channel power sequencers, and more particularly to a simple analog single-channel supply voltage sequencer that senses the voltage of a particular supply voltage rail (i.e., conductor) and accordingly controls enabling and disabling of another supply voltage rail(s), and which can be interconnected with other like supply voltage sequencers to establish various desired sequences of enabling and disabling of a desired number of supply voltage rails.
A power engineer may need to deal with multiple supply voltage rails in an application wherein particular sequences of powering up and powering down the multiple supply voltage rails are required in order to achieve proper operation of devices powered by the supply voltage rails or in order to avoid damage to certain circuit components thereof. The multiple supply voltage rails typically are connected to the outputs of corresponding voltage regulator circuits, such as low drop out (LDO) voltage regulators.
The reason for providing the power-up and power-down sequencing is to prevent particular supply voltage rail(s) from being powered up simultaneously and to prevent particular supply voltage rail(s) from being powered down simultaneously. Various simple conventional supply voltage sequencers are known as “voltage monitors”, “voltage supervisors”, or “voltage detectors” such as the one shown in Prior Art FIG. 1. Examples of simple commercially available simple single-channel voltage monitors, and the like include the assignee's TPS3808 and TPS386000 and Analog Devices' ADM1085.
Much more complex supply voltage sequencers for sequencing a relatively large number of supply voltage rails also are commercially available. Such complex sequencers typically include digital processing circuitry, and are unacceptably costly for use in applications in which there are only a few supply voltage rails that need to be sequenced. Furthermore, some complex digital supply voltage sequencers contain state machines which may not be fail-safe in the presence of certain conditions such as electrical noise and during time intervals in which a supply voltage is significantly reduced. (For example, electrical noise may cause state registers inside the state machine to change state, and logic circuitry may lose logic information therein as a result of electrical noise.) Examples of more complex commercially available supply voltage sequencers include Texas Instruments' UCD9080 8-channel power supply sequencer and monitor, Linear Technology's LTC2924 quad power supply sequencer and Maxim's MAX16050 and MAX16051 sequencer circuits.
Prior Art FIG. 1 shows a conventional simple supply voltage control circuit of the kind typically referred to as a “voltage monitor”, “voltage supervisor”, or “voltage detector”. In FIG. 1, an enable input of a first voltage regulator LDO#1 receives an input enable signal EN1 and generates a regulated output voltage VOUT1 in response to enable signal EN1. A voltage regulator output signal VOUT1 is applied to the input of a “supervisor I/C circuit” which generates another enable signal EN2, after a predetermined delay. Enable signal EN2 is applied to the input of a second voltage regulator LDO#2 which generates a second regulated output voltage VOUT2. As indicated by the waveforms shown in FIG. 1, delay through the supervisor I/C circuit causes the powering up of VOUT2 to be delayed relative to VOUT1 . A user of the power control circuit in Prior Art FIG. 1 may switch first enable input signal EN1 from a high state to a low state to “disable” VOUT1, i.e., “power VOUT1 down”.
A disadvantage of the simple supply voltage control or sequencer circuit of Prior Art FIG. 1 is that it does not provide the ability to power-down VOUT2 before powering down VOUT1, which may be required in some applications. Furthermore, the supply voltage control circuit of Prior Art FIG. 1 also does not provide the ability to set a percentage of the threshold target voltage of VOUT1, e.g., 10%, at which VOUT1 is considered to be powered down.
Consequently, there is no capability for the user to wait until VOUT1 falls to its 10% threshold level before beginning a power down of VOUT2. Therefore, if a user wants the foregoing capabilities in a simple supply voltage sequencing system, the user must provide additional customized (and therefore expensive) circuitry in order to detect the 10% point of VOUT1 and then generate EN2.
Thus, there is an unmet need for an inexpensive, simple, single-channel sequencer that can be interconnected with other like single-channel sequencers to provide multiple-channel sequencers that can provide various desired power-up sequences and various desired power-down sequences for multiple supply voltage rails, respectively.
There also is an unmet need for an inexpensive, simple, analog single-channel sequencer which is capable of monitoring the occurrence of pre-determined upper and lower threshold levels of a supply voltage rail.
There also is an unmet need for an inexpensive, simple, single-channel sequencer that can be interconnected with other like single-channel sequencers to provide multiple-channel sequencers which are capable of monitoring the occurrence of pre-determined upper and lower threshold levels of corresponding supply voltage rails and accordingly providing various desired power-up sequences and various desired power-down sequences for the corresponding supply voltage rails, respectively.
There also is an unmet need for an inexpensive, simple, single-channel sequencer that can be interconnected with other like single-channel sequencers to provide multiple-channel sequencers having only a desired number of channels, to avoid the cost of using complex digital multiple-channel sequencers which include more channels that are needed.
There also is an unmet need for an inexpensive, simple, single-channel sequencer that does not contain a state machine which may be subject to noise-induced logic errors.